1. Field of the Invention
This invention relates to fiber optics and more particularly to a method and apparatus for optical fiber transmission in a utility conduit containing a hostile fluid.
2. Description of the Prior Art
Optical fibers are a particularly valuable transmission medium in the communication arts because of their well-known broad bandpass characteristic and, of course, because of their ability to carry signal frequencies in the light wave region of the frequency spectrum. Unfortunately, however, optical fibers are expensive or inconvenient to use in many applications because of their tendency to fail or to degrade in performance when subjected to mechanical stress under hostile environmental conditions, such as exposure to high humidity, water, oil or gas, for example. When exposed to such hostile conditions, even the slightest perturbations of the optical fibers, such as microbends, for example, may significantly increase the optical transmission loss factor of the cable and also degrade its bandpass characteristic.
Because of the aforementioned characteristics of optical fibers, they are not easily introduced into conventional pipes, tubing or other conduits which contain water, gas or oil. When the optical fibers are introduced into such piping systems or other conduits, they are, of necessity, bent or subjected to other mechanical stresses which lead to their ultimate performance degradation and failure. Accordingly, when optical fibers are introduced into existing piping systems or other conduits, resort must be had to expensive non-flexible metallic shields or armored cable which limit the mechanical stresses placed on the optical fibers and also their exposure to hostile environments. Considering the vast network of piping systems which exist in the world today for the distribution of utilities, such as water, oil and gas, for example, it is apparent that a need exists for optical fiber transmission apparatus which would make use of this existing piping network and which would not require the use of the aforementioned armored cable or other shielding devices.